This invention relates to a control system for a mobile, self-propelled holster capable of travelling in orthogonal directions for transporting a die assembly into and out of a press in the act of a change from one die assembly to another.
Mobile dies bolsters are usually propelled either electrically or pneumatically. Either propelling method has its own advantages and disadvantages. The electrical propelling method is the more widely accepted by virtue of the ease of automation. A problem arises, however, as the die bolsters have recently been equipped with die lifters and lower-die clamps with a view to the automation of, and the curtailment of the period for, the procedure preparatory to actual pressing operation. The use of hydraulic pressure is preferred for operating the die lifters and lower-die clamps becauuse of the less space requirement of the hydraulic power system. In electrically propelled die bolsters, however, the hydraulic power system demands an additional electric motor as well as solenoid valves for its operation. Consequently the power cables for feeding the electrical equipment on the die bolsters must be of special construction and so lack universality.
An additional drawback of the electrically propelled die bolsters also concerns the power cables, which are required to carry current at a voltage ranging from 200 up to 400 volts. Should they be accidentally broken or otherwise impaired, therefore, the consequences can be serious.
The above problems are absent from pneumatically driven die bolsters, but a different set of problems manifest themselves. One of these is that their control systems have not been sufficiently safeguarded against operating errors. The operator has had to rely on his own skill in manipulating the controls. These controls have been placed on the bolster itself, moreover, so that the operator has been in constant exposure to danger as he operates them.